CRISPR gene editing

CRISPR is short for clustered regularly interspaced short palindromic repeats, referring to repeated DNA sequences first studied in bacteria and other microbes. In naturally occurring CRISPR immune systems, RNA molecules derived from these sequences help guide CRISPR-associated proteins toward genetic material from previously encountered viruses. Researchers adapted this targeting system as a way to study and change DNA. In 2012, a study by Martin Jinek and colleagues showed that the Cas9 enzyme could be directed by engineered RNA to cut chosen DNA sequences, helping establish a programmable genome-editing method. CRISPR is a family of systems; Cas9 is its best-known editing enzyme, not the only possible one.

A typical CRISPR-Cas9 experiment pairs Cas9 with a guide RNA designed to bind a selected DNA sequence. After the complex reaches a compatible target, Cas9 cuts the DNA. The cell's own repair machinery then reconnects the strands. Repair without a supplied template can introduce small insertions or deletions that disrupt a gene; when a suitable DNA template is provided, researchers may use repair to make a specified change. The guide helps direct the system, but does not by itself dictate every outcome: repair can be unpredictable, and related but unintended DNA sites can sometimes be altered. Other CRISPR enzymes and modified editors use different mechanisms, so not every CRISPR-based tool makes the same kind of cut.

In laboratories, genome editing can help researchers test what genes do, model disease and investigate how cells respond to genetic changes. Potential applications also include agriculture and medicine, although technical feasibility and evidence differ by use. A clinical example is Casgevy, which the U.S. Food and Drug Administration approved in 2023 for certain patients aged 12 and older with sickle cell disease and recurrent vaso-occlusive crises. The treatment uses CRISPR-Cas9 to edit a patient's blood-forming stem cells outside the body. After conditioning chemotherapy, the edited cells are returned to the patient; they are intended to increase fetal hemoglobin, which can reduce sickling. This is a specific, intensive treatment—not a general method for editing every cell or curing every inherited condition.

A targeted design does not eliminate the possibility of unintended edits, and results can depend on the DNA sequence, delivery method, cell type and repair process. In medicine, each proposed use therefore needs evidence about its safety and effectiveness; CRISPR is a tool, not a treatment whose benefits are automatic. Most current therapeutic editing targets somatic cells, such as a patient's blood cells, and is not passed on to that person's children. Editing eggs, sperm or embryos could create heritable changes, raising additional questions about safety, future generations, consent and social impacts. The National Academies has emphasized that decisions about human genome editing involve scientific evidence as well as ethical governance and public engagement.

In 2012, Jinek and colleagues published a demonstration of programmable, RNA-guided Cas9 DNA cleavage. In 2020, Emmanuelle Charpentier and Jennifer Doudna received the Nobel Prize in Chemistry for developing a method for genome editing using CRISPR-Cas9. In December 2023, the FDA approved Casgevy, the first U.S.-approved therapy to use CRISPR/Cas9. These milestones trace a shift from understanding a microbial defense mechanism to using related molecular tools in research and a limited number of medical applications.